1. Field of the Invention
The present invention relates to an organopolysiloxane composition useful as a sealant or the like, the cured product of the composition being excellent in mildew resistance and its durability as well as excellent in heat resistance and weathering properties such as resistance to ultraviolet light, thus hardly undergoing discoloration.
2. Description of the Prior Arts
Since room temperature curable (RTV) organopolysiloxane compositions capable of being crosslinked by moisture contained in the air have good handleability and the cured products thereof are excellent in weathering properties and electric properties, they are used in sealants for construction, adhesives in electric and electronic fields, and the like. Particularly, deoxime type RTV organopolysiloxane compositions have a good adhesion to various adherends even at places where, for example, water is frequently used or a large amount of moisture exists, such as kitchens, bathes and lavatories in houses.
On the other hand, with an improvement in construction techniques of houses in recent years, air tightness of houses have been also improved. Thus, said places where water is frequently used or a large amount of moisture exists are suitable habitats for microorganisms such as mildew or mold. Particularly, mildew or mold extends its hyphae even into the inside of RTV silicone rubber, so that it is difficult to remove mildew or mold by application of chemicals, much less by wiping, the appearance of the silicone rubber is often impaired.
As a solution, a mildew proofing agent is kneaded into sealants. Particularly, for silicone sealants, in view of safety as well as mildew resistance, thiazole compounds (Japanese Pre-examination Patent Publication (kokai) 54-127960), benzimidazole compounds (Japanese Pre-examination Patent Publication (kokai) 54-43260 and 56-38348), etc. are proposed. However, silicone sealants containing these mildew proofing agents have insufficient mildew resistance.
In the Japanese Pre-examination Patent Publication (kokai) 2-306907, it is proposed to use p-chloro-m-xylol and bis(2-pyridylthio-1-oxide) zinc salt in combination for modified silicone sealants. However, the sealants containing the mildew proofing agent have a problem that they tend to turn yellow upon exposure to heat or ultraviolet light. Particularly, this tendency is more serious when the mildew proof agent is added in a large amount to deoxime type RTV silicone rubber compositions containing an aliphatic unsaturated group-containing silane. For this reason, it is impossible to increase the amount of the mildew proofing agent in such a way that the mildew proofing agent is effective for all types of mold or mildew without yellowing
In the Japanese Pre-examination Patent Publication (kokai) 6-40821, it is proposed to use bis(2-pyridylthio-1-oxide) zinc salt in combination with a benzimidazole mildew proofing agent for improving discoloration and long-term mildew resistance. However, durability of the mildew resistance is still insufficient, and in particular when a hydrolyzable silane containing aliphatic unsaturated bonding is used as a curing agent, durability and discoloration are not improved sufficiently.